Discussion of the Background
Solvents are widely used in manufacturing processes as cleaning agents. In the past, used solvents have been discarded. However, as the disposal costs for toxic chemicals has risen, it is now imperative that toxins such as solvents are recycled and reused as much as possible.
Organic solvents, such as tetrahydrofuran (THF), are widely used in the area of photoconductive drum manufacturing for photocopiers or printers. For example, a photoconductive drum is commonly coated with a charge-transport material (CTM), and an appropriate binder resin. The CTM is usually a low molecular weight organic compound, and the binder resin generally belongs to the class of aromatic polycarbonates (PCR). After the CTM and the PCR are applied to the photoconductive drum, which typically includes a hollow metal cylinder substrate, the edges of the drum are cleaned with an organic solvent such as THF. The use of THF in manufacturing photoconductive drums and in manufacturing other products results in a large amount of used THF that has heretofore been discarded.
Although THF is a useful solvent, it has the drawback of forming explosive vapors (such as peroxides) when it is exposed to oxygen. Therefore, THF has a limited shelf life and can be difficult to reuse in that if THF is reused for cleaning purposes, it is likely to begin producing explosive vapors after a predetermined amount of time.
In order to reduce the likelihood of the production of explosive vapors, free radical scavenger substances such as butylated hydroxy toluene (BHT) have been added to organic solvents, such as THF, in order to stabilize the solvent and prevent formation of peroxides when the solvent is exposed to oxygen. However, as THF is exposed to oxygen, BHT is depleted over time, leading to the formation of explosive vapors, for example, in a container holding THF. Therefore, THF is commonly discarded after it is used for a predetermined amount of time.
Under current U.S. and state/local regulations, a generator or source of hazardous waste, such as solvents, must track the amount of waste generated and submit forms reporting the amounts disposed of to the federal and/or state EPAs, depending on the amount of waste produced. Furthermore, A "Hazardous Waste Manifest" may require the generator of the waste to certify that they have a program in place to reduce the volume and toxicity of waste generated to the degree economically practicable and that they have selected the practicable method of treatment, storage, or disposal currently available which minimizes the present and future threat to human health and the environment. See, e.g. EPA Form 8700-22, Item 16 (Rev. 11-88). Moreover, hazardous wastes are often costly to dispose, and a disposal company is often retained to transport and adequately dispose of the waste. The discarded solvent must then be replaced with additional solvent, and thus additional solvent costs are incurred. Therefore, there is a need for a safe and efficient method for recovering and recycling toxic/hazardous wastes such as solvents.
It has been known to recycle solvents through a method of vaporizing the solvent through heating, and condensing the vapor in a known condenser. However, such a method poses a substantial risk of explosion when used for recycling volatile solvents such as THF. As described above, if THF is used and stored for a predetermined amount of time, the BHT is depleted and volatile vapors form. Therefore, THF has not heretofore been recycled utilizing a distillation process. Thus, there remains a need for a method and apparatus for safely recycling a volatile solvent that does not pose a risk of the formation of explosive vapors, so that the solvent can be reused.